Answer

Hi David,
I am very sorry for the delay in getting back to you. It does sound like Abbie may have had some type of flea or other allergy to begin with. In stopping inflammation (which causes itching), steroids can also suppress the immune system, causing secondary infections. The ovals sound like a superifical skin infection, which is not uncommon. The antibiotic (probably a cephalosporin), is to help her fight the infection, a safe bet even if it doesn't look like one, for the reason below. They also may have been testing for a parasitic infection, like mites that live under the skin, as opposed to a bacterial infection. Cultures for fungus are also sometimes performed. It's hard to say what they were testing for, unless you know what they did to test?
I do find in some cases, the two need to be give at the same time. The infection, probably from the steroid is itchy, but chewing starts that cycle of reinfecting themselves. Stopping the cycle is key, because these can develop into "hot spots", or much bigger areas of infection that also look moist.
The only thing I would probably do different is clip up the affected areas so hair doesn't get in there, finish the antibiotics, and possibly put her on a topical medication, with or without an E-collar to prevent her from chewing at it.
If antibiotics, and possibly a second round of steroids with the additional discouraging from chewing do not help, a biopsy may be in order. Biopsies don't just look for cancer, but usually in the skin, it's more to confirm or deny that it's allergy/fungal/bacterial related, and make sure it's not an autoimmune disease (which in that area, it's probably not).
I hope this has helped, and I again apologize for the delay. If you have any further info or questions, please let me know. Good luck!
Dr. Chenoa